Background: pesticides have been associated with Parkinson's disease (PD), but there are few data on important exposure characteristics such as dose-effect relations. It is unknown whether associations depend on clinical PD subtypes.
Objectives: we examined quantitative aspects of occupational pesticide exposure associated with PD and investigated whether associations were similar across PD subtypes.
Methods: as part of a French population-based case-control study including men enrolled in the health insurance plan for farmers and agricultural workers, cases with clinically confirmed PD were identified through antiparkinsonian drug claims. Two controls were matched to each case. Using a comprehensive occupational questionnaire, we computed indicators for different dimensions of exposure (duration, cumulative exposure, intensity). We used conditional logistic regression to compute odds ratios (ORs) and 95% confidence intervals (CI) among exposed male farmers (133 cases, 298 controls). We examined the relation between pesticides and PD subtypes (tremor dominant/non-tremor dominant) using polytomous logistic regression.
Results: there appeared to be a stronger association with intensity than duration of pesticide exposure based on separate models and a synergistic interaction between duration and intensity (p-interaction = 0.04). High intensity exposure to insecticides was positively associated with PD among those with low intensity exposure to fungicides and vice versa, suggesting independent effects. Pesticide exposure in farms specialized in vineyards was associated with PD (OR = 2.56; 95% CI: 1.31, 4.98). The association with intensity of pesticide use was stronger, although not significantly (p-heterogeneity = 0.60), for tremor dominant (p--trend < 0.01) than for non-tremor dominant PD (p--trend = 0.24).
Conclusions: this study helps to better characterize different aspects of pesticide exposure associated with PD, and shows a significant association of pesticides with tremor dominant PD in men, the most typical PD presentation.